User profile transfer to AAD account

How does one connect the users AD (or local) user profile to the user after joining the PC to Azure.
The user (even when using exactly the same user name) does get a completely blank profile.
- Some people actually panic when we try this. "Everything is gone :-(" as one manager said today.

I've been going through everything MS doc on this and asked our cosultant who claims it's by design.

- And yes I do know data is on OneDrive but in some cases this is years of customizing your workplace just gone.

I'm sure someone has figured out how to remedy this?
 
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